From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 23FEF54CF6D for ; Tue, 22 Sep 2026 13:55:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790085323; cv=none; b=HAe1gbzQDcjFbAdjNu+sMQn1kA4aVZrs7EuuOQhcrzsZn0bQYAtmbxBdGXhV5i58oJAWCbKQDkXczQ0DfC1R7d72jCe/G2hgw+TWq+lK5ByFR5k1L8mEel9CtBBpUoMptczknCSF6sTkfTruD+DXLcRyl/r5GyyGAFktLPnu+ao= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790085323; c=relaxed/simple; bh=QZTOW61nSZeY4QySSez/VRixUxc1jj2lCafwqWmQ5pw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=WypJecfIHb8kR7D16MVNF8u85Oe084mOdEItxc1gRc3HMjCD+Dlv1/o3GgVsTEbPXB8GIV3hK4O1RqnIIUu+l/rdx7j647OZGFBflxLzbb7NO1o2vA9WD7G1jpBh3SKI4Nj6mKFggiCxvdVpJK7h960+sZXCiN4JuWZd8MobtZo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WlD8MKaU; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="WlD8MKaU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E1B041F000FF; Tue, 22 Sep 2026 13:55:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790085321; bh=vAErR5nUF5jYNRVD6fb923LvqrMdmDoaO1mDvYNJTgo=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=WlD8MKaUgx0yamc8h91fzZpUq+67Jj9i2OaP2jc0DoDFTbLwN9NDh1giPE8DcEJAz 8QWzyr2rLUvwsXjaUtU6g7x2xqFukPXEX5DFPVrrWpAp8KVHpLmXAfibyQaYG0DoHu X2n7EiLG27ZV6U4BpIQotcFuxlULVn6OWfchYpZncZeDU2n2fXWOiiDF+NvyfxOdLu ZMxE6Bl8h5EHVZd78B1q8CztRTwFAtCeqaT28dtbKsRpowV0rEIATOCZYAw14xPuo8 3Q0h0CLxLrJbKw1Fi34UpGfNSNU02cwvUYxH+xXZJUoUr4mYQ+0YEVE3GZkw5TFyzW lwkbI4TJnWnjg== Message-ID: <462b217c-a422-4818-bac1-7f204f32fa29@kernel.org> Date: Tue, 22 Sep 2026 15:55:13 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 0/2] mm/memory_hotplug: optimize zone contiguous check when changing pfn range To: Yuan Liu , Oscar Salvador , Mike Rapoport , Wei Yang Cc: linux-mm@kvack.org, Nanhai Zou , Chen Zhang , Jason Zeng , Chen Yu , Pan Deng , Tianyou Li , linux-kernel@vger.kernel.org References: <20260920084946.3266279-1-yuan1.liu@intel.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/20/26 10:49, Yuan Liu wrote: > This series introduces a pages_with_online_memmap member into struct > zone to avoid pageblock-by-pageblock scans across the entire zone and > improve memory hotplug performance. > > Approach > ======== > Add a new zone member, pages_with_online_memmap, that tracks the > number of pages within the zone span that have an online memory map, > including present pages and memory holes whose memory map has been > initialized and for which pfn_to_online_page() succeeds. > > For early boot memory, pages_with_online_memmap is calculated in > memmap_init_zone_range(). PFNs initialized by memmap_init_range() are > included in pages_with_online_memmap, and hole PFNs for which > pfn_to_online_page() succeeds are also counted in > init_unavailable_range(). For hotplugged memory, > pages_with_online_memmap is updated through adjust_present_page_count(), > which is called during memory online and offline operations. When > spanned_pages == pages_with_online_memmap, every PFN in the zone span > has a valid memmap entry, so pfn_to_page() can be called for any PFN > within the zone span without an additional pfn_valid() check. > > Note: this counter may temporarily undercount when pages with an > online memory map exist outside the current zone span. Such pages > are only created during boot, when initializing the memory map of > pages that do not fall into any zone span. The undercount itself > can only happen after boot, during memory hotplug, when growing > the zone to cover such pages and later shrinking it back, which > may result in a "too small" value. This is safe: it merely > prevents detecting a contiguous zone. > > The contiguity check using pages_with_online_memmap is stricter than > the old pageblock-by-pageblock scan. The old set_zone_contiguous() > iterated at pageblock granularity via pageblock_pfn_to_page(), so a > zone could be marked contiguous even if a subsection-sized hole > existed within a pageblock. The new check requires > spanned_pages == pages_with_online_memmap, meaning every PFN in the > zone span must satisfy pfn_to_online_page(). > > Performance > =========== > 1. For VM hotplug performance data, please refer to Patch 2. > 2. This series also benefits CXL hotplug. Performance results are > as follows > https://lore.kernel.org/all/20260409023552.GA2807@AE/ > > Tested cases > ============ > 1. Hotplug/unplug correctness with both online_movable and online > policies, including partial unplug, middle-block offline gaps, and > edge-block span shrink. > 2. Large scale (256G/512G) plug/unplug performance. > 3. Boot-time subsection holes (aligned/unaligned, in-zone and > cross-zone) with correct pages_with_online_memmap accounting. > 4. kernelcore=mirror: verified no overcounting. > > Patch overview > ============== > Patch 1 makes shrink_zone_span() more robust when memory/hole boundary > falls within a subsection. It checks the full subsection range to avoid > incorrectly shrinking the zone span during memory unplug. > > Patch 2 introduces pages_with_online_memmap to replace > pageblock-by-pageblock scans across the entire zone for zone contiguity > checks. > > v10 changes: > 1. Rebased onto v7.3-rc3. > 2. Added Acked-by: Mike Rapoport (Microsoft) on patch 2 and reworded > the init_unavailable_range() comment as suggested. Thanks, I'm planning on queuing this tomorrow. -- Cheers, David